Not only does sediment spread horizontality and from youngest (top) to oldest (bottom), it also continues to spread flat in all directions until it either runs out of material—pinches off—or hits a barrier. this is known as the

law of original horizontality
law of superposition
law of original lateral continuity
law of gravity and oppositional force
law of cross-cutting relationships

law of superposition

Explanation:

The law of superposition in geology suggests that the sediments are spreading out in a horizontal manner, flat, in all directions, until there's some natural feature that will stop them. It also suggests that the sediments are arranged vertically from the oldest being at the bottom, and the youngest layers being on the top.

Even though this is not always the case in nature, still there are lot of examples that support the law of superposition. When the sediments are aligned in that manner, the geologists find it very helpful and easy to determine the relative age of the layers, as well as the relative age of the fossils that are found in them.

oceans

indian ocean

pacific ocean

atlantic ocean

arctic ocean

southern ocean